The present invention refers to abrasive grain agglomerates on the basis of abrasive grains from the group of conventional abrasive grains, such as for example, corundum, fused corundum, sinter corundum, zirconium corundum, silicon carbide and boron carbide as well as from the group of the super abrasives, such as for example, cubic boron nitride and diamond, and/or mixtures thereof, whereby fine abrasive grains are bonded into compact abrasive grain agglomerates by means of an inorganic binder.
The present invention also refers to a method for the production of such abrasive grain agglomerates and their use in abrasives.
Abrasive grain agglomerates have been known in many variations for a long time and are normally utilized in bonded abrasives such as for example, abrasive disks or coated abrasives such as for example abrasive belts. Abrasive grain agglomerates are normally constructed from single abrasive grains, the primary particles which are bonded into an abrasive grain agglomerate by use of a binder. Binders are either organic or inorganic binders, whereby oftentimes organic binders are phenol resins, while inorganic binders can be ceramic binder materials.
The big advantage of abrasive grain agglomerates is that finely grained abrasive grains can be utilized as primary particles from which the agglomerate grain is then built, which, as compared to the a single grain of the same size, has a completely different degradation mechanism during the abrading process.
While a single grain of comparable size, depending on the pressure conditions during the abrading process, normally becomes dull or becomes destroyed, the abrading conditions with abrasive grain agglomerates can be purposefully selected so that single (worn-out) grains break from the bond formation so that always new cutting edges are formed such that on the one hand, the agglomerate grains retains a long life span and on the other hand, exhibits a cool and homogenous polished pattern. A further advantage of the abrasive grain agglomerates is that finely grained abrasive grains can be utilized for abrading processes and abrading tools which otherwise would not be suitable due to their small grains size.
DE 103 92 532 B4 describes abrasive grain agglomerates which comprise a plurality of abrasive grains that are bonded with a binder material, wherein the binder material has a melting temperature between 500° C. and 1400° C. The DE 103 92 532 B4 also describes a method for the production of such abrasive grain agglomerates where the abrasive grains are mixed with a binding agent and subsequently are subjected to a heat treatment in a rotating tubular kiln between 145° C. and 1300° C. The abrasive grain agglomerates that are so obtained have a total porosity between 35% by volume and 80% by volume, whereby at least 30% by volume of the pores are connected. From this production method elongated agglomerates are obtained with a ratio of length to cross section of at least 5:1. Binders that are utilized are glass-type binder agents, ceramic materials, inorganic materials and combinations of the same. The so obtained abrasive grain agglomerates are most of all used in bonded abrasives in order to control the percent portion and the properties of the porosity in the abrasives and to preserve the porosity in the form of a permeable and connective porosity.
DE 10 2005 007 661 A1 describes abrasive grain agglomerates that are formed by means of a binder in material-interconnecting engagement, and which exhibit an approximately spherical outer shape and are supposed to possess a porosity of at least 35% by volume. These abrasive grain agglomerates are formed from single abrasive grains whose particle size is in the range between 0.05 μm and 10 μm, which are then joined into agglomerates with a diameter in the range between 10 μm and 150 μm. In the abrading tools, these agglomerates are utilized as narrow range classified with a quasi constant graining. As binders organic binders are preferably used, such as for example, phenol resins, polyurethane, epoxy resins, urea resins and poly vinyl butyral. These abrasive grain agglomerates are especially suitable for use in coated abrasives, where they are utilized for very fine abrading treatments of surfaces of work pieces.
The production of abrasive grain agglomerate is in principle quite easy and is mainly based on mixing the single grains with a binding agent so they form an abrasive grain agglomerate and are then subsequently heat treated. Depending on the type of the binding agent used, very different temperature conditions apply.
While with inorganic binding agents normally temperatures apply that are markedly above 500° C., the agglomerates with organic binding agents are normally hardened at relatively low temperatures—between 200° C. and 300° C.
The known inorganic binding agents have the advantage that they can form very strong bonds, which however always requires relatively high temperatures, so that inorganic binder systems are not suitable for temperature sensitive abrasive grains such as for example, eutectic zirconium corundum, cubic boron nitride or diamond, and are thus not used.
The organic binder materials on the other hand have the drawback that the bond itself is less strong. In addition, when using organic binders there is the problem that the mixtures from binders and finely grained abrasive grains have a tendency to stick to the edges of the apparatus. This requires rather high maintenance and cleaning efforts especially when an abrasive grain product change takes place because normally when producing abrasive grain agglomerates, the abrasive grains have to have a narrow grain size distribution. The contamination with larger grains would lead to considerable problems in abrading operations where the main object is a fine treatment of work piece surfaces, such as for example the treatment of decorative lacquer surfaces, where such impurities can lead to scratches which can only be eliminated, if at all, subsequent to the abrading operation and only with a considerable effort. With organic binding agents, aside from the contamination of the apparatus, there is also the issue of environmental problems, as the use of organic binding agents or binders are most often associated with foul smells and health risks.
Thus, the problem still exists to provide a binder system for abrasive grain agglomerates that do not suffer from these drawbacks.